1. Technical Field
Several aspects of the present invention relate to a semiconductor device, electro-optical device, and a method for manufacturing a semiconductor device.
2. Related Art
In recent years, electronic appliances that bend flexibly gained an increasing attention. Flexible displays, typically electronic papers, are light to carry, fits comfortably to one's hand, and have shock absorbability. Such apparatuses with these characteristics may potentially play an important role in ubiquitous society. Electronic devices with bendable organic thin film transistors (hereafter referred to as “organic TFT”) mounted on a flexible plastic substrate have been suggested for such electronic apparatuses. Refer to JP-A-2003-518756 for an example. The organic TFT allows the forming of transistor devices at room temperature in a normal pressure, thereby reducing a manufacturing cost. Moreover, substantial manufacturing cost savings may be achieved with applying general-purpose printing techniques such as inkjet and spin coat methods.
The field-effect transport speed of organic TFTs is slower than that of other TFTs by several factors. Therefore, if all the TFTs in the electronic devices are formed with organic TFTs, the performance of those devices unfortunately declines. In order to resolve such problem, other semiconductor devices with higher field-effect transport speed may be applied for drive circuits, and the organic TFTs are used only for some parts of the electronic device.
Low-temperature polysilicon thin-film transistors (hereafter abbreviated to “LTPS-TFT”), in particular, have a high field-effect transport speed. Thus, performance thereof does not decline even when the space the transistors take up in the electronic device is reduced. Such characteristics are suitable for making the electronic devices lighter and thinner, meeting the needs for resolving the above problem. However, a high temperature of 600° C. is required for manufacturing such LTPS-TFTs, making it difficult to form those LTPS-TFTs on a plastic substrate used for flexible devices.
The above problem is solved by a packaging technique called Surface-Free Technology by Laser Ablation/Annealing (SUFTLA; a registered trademark of Seiko Epson Corp.), in which the LTPS-TFTs created in advance on a glass substrate are transferred on a plastic substrate. Refer to JP-A-2003-297974 as an example of related art.
Referring now to FIG. 10, prior to the transfer step in SUFTLA, a plurality of device chips 4 to be transferred is formed in advance on a glass substrate 22, so that they are aligned in the same arrangement on the plastic substrate. FIG. 10 is a schematic plan view of the glass substrate 22 on which the device chips 4 are formed. An area R indicated in a dotted line is the area to be transferred to the plastic substrate in the single SUFTLA process. Generally, a pixel is formed in the center of the area R, constituting a display area. Thus, the device chips 4 are aligned in the perimeter of the area R, creating a dead space in a region in which the device chips 4 are not disposed. This significantly limits the number of device chips 4 that can be disposed in proportion to the area of the glass substrate 22, involving the problems of manufacturing cost increase, massive consumption of materials and energy, and imposition of substantial burden on the environment.